1. Field of the Invention
The present invention relates in general to an optical visualizing apparatus, and in particular to an optical visualizing apparatus such as an HMD (head mounted display) apparatus mounted in front of a viewer's face for viewing an image.
2. Description of the Related Art
In the related art, there has been proposed a typical optical visualizing apparatus for viewing images, such as video or television images, that are displayed on a pair of color liquid-crystal display panels mounted in front of the is face of the viewer and that are enlarged by means of an ocular lens.
A display unit for this type of optical visualizing apparatus comprises components embedded in a cabinet-like lens barrel. The components include a backlight, a transmitting-type liquid-crystal display device illuminated by the backlight and a reflecting mirror for reflecting an image output to the liquid-crystal display device to ocular lenses. An image output to the liquid-crystal display device is enlarged by the ocular lenses before being projected on the retinas of the right and left eyes of the image viewer.
Such an optical visualizing apparatus may be mounted on the head of the viewer or can be worn in the same way as spectacles.
However, external scenery can not be seen by a user wearing such an optical visualizing apparatus because the optical visualizing apparatus outputs an image directly in front of the eyes of the viewer. In order to see external scenery, a power-supply switch of the optical visualizing apparatus must be turned off or the concentration of the image must be adjusted by using an adjusting means, such as a concentration adjusting button.
FIG. 3 is a diagram showing an optical visualizing unit 4 employed in an optical visualizing apparatus provided by the related art. As shown in the figure, in the optical visualizing unit 4, typically an image illuminated by a light-source unit 12 serving as a light source of the liquid-crystal display device is reflected by a concave half mirror 19 to be seen as a virtual image. The outer surface of the concave half mirror 19 completes a transmitting-type half coating process. On the outer side of the concave half mirror 19, a liquid-crystal shutter 23 is provided for adjusting infiltration by beams coming from the external world.
FIG. 29 is a diagram showing the liquid-crystal shutter 23. As shown in the figure, the liquid-crystal shutter 23 is formed into a shape resembling spectacles. The spectacles portion is made of a liquid crystal 26a that is connected to a flexible connector 27 by a transparent electrode.
When the viewer wishes to see external scenery while he or she is viewing an image in the optical visualizing unit 4 equipped with such a liquid-crystal shutter 23, light coming from outside the apparatus is allowed to infiltrate into the optical visualizing unit 4 by adjusting the concentration of an image being viewed. While the concentration of the image is being adjusted, the entire liquid crystal of the liquid-crystal shutter is set to an opened state.
However, the optical visualizing apparatus of the related art has a problem that, when a suspending operation such as a mute operation is carried out, only the sound disappears but the image remains displayed or, even if both the sound and the image disappear, the external scenery can not be observed unless other operations are performed. In addition, there also arises another problem that while the image viewer is seeing the external scenery, the external scenery is inadvertently interrupted because the video and audio signals are still output to the viewer.
As a result, a problem which remains to be solved exists in how to process the image and the sound and how to control the state of the image after a suspend operation, such as a mute operation, has been carried out.
Also, the optical visualizing apparatus provided by the related art as described above also has a problem that, when the concentration of an image is adjusted, too much outside light enters the optical visualizing apparatus, providing too much interference to the image being viewed because the liquid-crystal shutter 23 for shielding the light coming from outside the apparatus has the same spectacles-like shape and the same size as the concave half mirror.